A Harvard-led study in the journal, Circulation, found people who drink two or more sugar-sweetened beverages a day have a 31% higher risk of early death from cardiovascular disease.

"Previous research has shown that sugar-sweetened beverages are associated with things like diabetes, weight gain, heart disease and stroke but what we didn't really look into was the increased risk of mortality or death," CBS News medical contributor Dr. Tara Narula told "CBS This Morning." "This research really did show that the more sugar sweetened beverages you drink, the higher the risk of death, primarily from cardiovascular death but also from cancer deaths, as well."

While Americans have been drinking fewer sugary drinks, such as soda and sports drinks, over the past decade, they still represent the single largest source of added sugar in the U.S. diet and their consumption is on the rise around the world.

For the study, researchers examined data from two different studies involving nearly 38,000 men and more than 80,000 women who were followed for 20 to 30 years. They were asked how much they ate and drank and what their lifestyle choices were like.

The researchers found that for those who drank one to two sugary drinks a day, the overall risk of death went up 14 percent. More than two sugar-sweetened beverages, that risk went up 21 percent.

"It's important to point out that this is the kind of study where we cannot say cause and effect," Narula said. "It is an association that they saw but definitely again adding to this body of evidence that sugar-sweetened beverages are not so great for our health."

The research also looked at the link between artificially sweetened beverages and death. The results showed no increase in mortality except for women who drank more than four of these beverages a day.

"More research is needed to look into that female effect," Narula said. "It may have been women that were overweight or obese were trying to switch to artificially sweetened beverages and they were already at high risk."

Last year, the American Heart Association recently issued guidelines on artificially sweetened beverages and concluded that they can be part of a healthy diet, especially for individuals who drink a lot of sugary drinks and want to cut back. But of course, water is still the healthiest choice.

"Drinking water in place of sugary drinks is a healthy choice that could contribute to longevity," Vasanti Malik, Sc.D., lead author on the paper and a research scientist in the Department of Nutrition in the Harvard T.H. Chan School of Public Health in Boston, Massachusetts, said in a statement. "Diet soda may be used to help frequent consumers of sugary drinks cut back their consumption, but water is the best and healthiest choice."